1. Field of the Invention
The present invention relates to an emulsion ink for stencil printing. More specifically, the present invention relates to an emulsion ink for stencil printing which can provide printed images (or printed pictures) having a high concentration and a constant quality despite of the type of printing papers and irrespective of presence or no presence of unevenness on the surface of printing papers, and causing no bleeding, no strike through, and no offset of printing ink.
2. Description of the Prior Art
In a stencil printing, a plate-making is first carried out by using a stencil printing master sheet and then ink is supplied through the perforations formed in the master sheet to print a body to be printed such as paper. Since preparation of perforated stencil printing sheets is easy, stencil printing is used in diversified applications.
As the ink used for stencil printing, water-in-oil (W/O) emulsion inks are generally used. Drying of these emulsion inks are carried out by splashing water components in the air and at the same time permeating ink components into printing paper to be printed (Unexamined Japanese Patent Publication Nos. 61-255967, 64-14284, 4-132777, and 5-117565).
However, with conventional W/O emulsion inks, ink components permeate into printing paper when the ink is dried, and at the same time, a colorant also permeates into the printing paper. Accordingly, there are problems that the amount of the colorant remaining on the surface of the paper is decreased and thus printing concentration is reduced. Besides, since the colorant in the ink permeates into the printing paper, so called strike through phenomenon in which reversed printed images can be seen through a back surface of the paper is easy to occur.
Further, since the permeation rate of ink components into the paper is varied depending on the type of papers, there are problems that the concentration of printed images to be obtained, and the extent of bleeding, strike through, and offset of ink are varied according to the type of papers. That is, when the permeation rate of ink into paper is high, ink components permeate into the paper with almost no ink remaining on the surface of paper. Thus, printing concentration is decreased and strike through of ink is increased, whereas offset of ink is decreased since ink components will not remain on the surface of paper. On the other hand, when the permeating rate is low, since ink components tend to remain on the surface of paper, printing concentration of printed images is increased and strike through is reduced. However, the offset is increased since a large part of ink components remain on the surface of paper.
Accordingly, it has been desired to provide an emulsion ink for stencil printing which can provide printed images having a high concentration without being affected by permeation rate of ink into printing paper, and at the same time causing no strike through and offset of ink.
Still further, since drying of emulsion ink is performed by permeation of ink components into paper, when stencil printing is conducted by using a sheet of paper having unevenness on its surface, it becomes difficult to obtain printed images of gloss tone depending on the type of paper. Such phenomenon can be observed even with a high grade paper (wood free paper) and medium grade paper, and particularly with low grade paper. Accordingly, quality of printed images to be obtained is varied depending on presence or no presence of unevenness on the surface of paper, and such phenomenon remarkably appears particularly when full color printing was performed.
Moreover, in stencil printing, since ink is extruded through perforations to supply it to printing paper, the ink must have been imparted with a certain extent of viscosity. When the impartment of viscosity is achieved with a macromolecular compound such as a resin to be contained in an oil phase, the rate of permeation of ink is decreased and the strike through becomes easy to occur.